1. Field of the Invention
The present invention relates to optical devices and to processes for fabricating optical devices generally, and, more particularly, to low-loss optically active devices exhibiting reduced losses and to processes of fabricating optically active optical devices.
2. Description of the Related Art
In forming optically active devices such as an optical modulator or an optical switch using optical polymer, an optical waveguide formed in the device is constituted of cores and upper and lower clads surrounding the cores. Here, the refractive index of the material used for the core is always greater than the refractive index of materials used for the clads. This difference in refractive indices makes the light passing through the core travel along the waveguide due to total internal reflection. Optical polymer is conventionally used in fabricating optically active devices non-linear characteristics. Typically, all core regions of the waveguide formed in the device are made of non-linear optical polymer. An exemplary structure may be found, for example, in the Electro-optic Channel Waveguide of J. I. Thackara, et alii, U.S. Pat. Nos. 5,006,285 and 5,007,696. If, as indicated for example, by the Nonlinear Optical Device For Controlling A Signal Light By A Control Light of K. Tajima, U.S. Pat. No. 5,191,630, all of the core regions of the waveguide forming an active device are made of non-linear optical material such as a non-linear optical polymer, we have noticed that the overall device loss characteristics are degraded. The waveguiding loss of a waveguide made of non-linear optical polymer exhibits a characteristic of about 0.5-1.0 dB/cm, and the waveguiding loss of the waveguide made of linear optical polymer exhibits a characteristic of about 0.1-0.2 dB/cm. Therefore, in the case of forming a waveguide having the same length and configuration with each other, a waveguide made entirely of only the non-linear optical polymer have disadvantages due to the substantial, and in our opinion unnecessary injection losses of the device, compared to the case of forming a waveguide made of the linear optical polymer. Directional coupler type optical switches and conventional Mach-Zehnder type optical modulators (e.g., the Hybrid All Optical Silica Waveguide Modulator Using Non-linear Electro-optic Components of J. Leonard, U.S. Pat. No. 5,546,480; the Mach-Zehnder Type Electro-optic Polymer Modulator In Which An Initial Output State can Be Controller By Post-photobleaching, of W. Y. Hwang, et alii, U.S. Pat. No. 5,692,075), as well as such devices as the Capillaiy Non-linear Optical Waveguide Device of L. M. Hayden, U.S. Pat. No. 4,887,884, conventionally have all regions in the waveguide including the electrode regions, formed of non-linear optical polymer that exhibits a comparatively higher optical loss than does linear optical polymer; consequently, the overall injection loss of the device is substantially increased.